Thermal polymerization initiators are required for a number of dental materials that polymerize under conditions in which initiation of polymerization by light is inefficient. Frequently, thermal setting dental cements are used for the adherence of ceramic or metallic restorations. Also the application of more opaque materials makes a self-curing thermal polymerization initiator necessary. Advantageous is a thermal polymerization initiator in cases when a polymerization in the depth is required or a larger quantity of material is used, such as for a temporary crown and bridge material. A large number of thermal setting materials comprise peroxide/amine initiators; most of them comprise BPO or modified BPO and amines. Only in individual cases other redox-initiators are used, such as peroxide/metal ions (reduction agents such as ascorbic acid), or metal carbonyl compounds/organic halogenides, or boralkyle compounds/oxygen, or persulfate/mercaptane, or sulfinate/metal compounds. Dental materials must fulfill some special conditions for patient comfort, convenience and safety. Polymerization of dental materials must occur at relatively low temperatures (about 37° C.) in bulk with high rates of polymerization and high degree of polymerization (resulting in at most a minute percentage of residual monomer). They should have a long shelf-life for a period of at least 18 month, which means that they should be thermostable at ambient temperature and do not decompose under moisture conditions. Furthermore, the oxygen inhibited layer should be minimized.
The commonly used dibenzoyl peroxide/amine initiator systems have the advantage of a rapid polymerization of monomers and a relatively thin oxygen inhibited layer. Furthermore, such initiators resist moisture. Disadvantages of commonly used dibenzoyl peroxide/amine initiator systems are the thermal-self decomposition of dibenzoyl peroxide (BPO) and the discoloration of the aromatic amines used. Due to the thermal decomposition of BPO the useful life-time (storage period after which the composition remains useful) of a prior art dental/medical composition is very short.
It is well known that other peroxides than dibenzoyl peroxide do not react with amines (J. Lal et al., J. Polym. Sci. 24 (1957) 75). Furthermore, a number of other initiator systems consisting of BPO or peroxides with a higher thermostability than BPO and metal compounds are used. But these systems are more influenced by oxygen therefor they are forming larger oxygen inhibited layers than peroxide/amine systems. The influence of oxygen is reduced if reductants such as glucose or ascorbic acid are used as coinitiators. Recently, a polymerization initiator was described comprising a peroxide, a metal salt and ascorbic acid (J. M. Antonucci et al., J. Dent. Res. 58 (1979) 1887; U.S. Pat. No. 404,402). Using this initiator dental materials were obtained having high mechanical properties. Disadvantageous is the self-oxidation of ascorbic acid due to moisture. Consequently, the initiator system losses a part of the coinitiator. Due to the oxidation of ascorboc acid the system discolorates intensively yellow. Further experiments were done using barbituric acid or thiobarbituric acid (U.S. Pat. No. 5,166,117). Polymerization initiators comprising BPO, a sulfinate and an amine were used by Kurraray (EP 0115410, 0115948, 0120559, 0277413). As sulfinate were used benzolsulfinate and as amine N,N-di-(hydroxyethyl)-p-toluidine. Polymerization initiators comprising of sulfinate/metal ions are suitable for production of artificial teeth, inlays and onlays. Furthermore the are usable in dental composites comprising MMA/PMMA. Disadvantageous is the bulk polymerization of methacrylates with this initiator due to the formation of an unpolymerized layer between the tooth and the polymer, which avoid the adhesion to teeth tissues. Bredereck had used as polymerization initiators inorganic salts of sulfinic acid, hydrohalogenides and some times peroxide (DE 1 003 448). Recently, a polymerization initiator was described consisting of cumen hydroperoxide, saccharin, copper or iron saccharinate an N,N-di(hydroxyethyl)-p-toluidine without evidence of the suitablity for technical applications (J. Appl. Polym. Sci., Part A, Polym. Chem. 32 (1994) 1459, 1470). In both publications it is shown that the effectivity of the initiator strongly depends on the participants of the initiator system. Only an exchange of copper saccharinate against iron saccharinate lead to a degree of the constant of polymerization of about 2 orders by magnitude. The concentration of the compounds of the initiator system are to low for dental/medical application.
One of the main desires of the prior art has been to find an efficient thermal polymerization initiator that has a long term thermal stability and a long term moisture stability. provides an efficient thermal polymerization initiator that has a long term thermal stability and a long term moisture stability.
Substituted as used herein refers to a fully or partially a halogen substituted moiety.
Unsubstituted as used herein refers to a moiety in which hydrogen is not substituted for by other atoms.
Alkyl as used herein refers to a paraffinic hydrocarbon group.
Alkylene as used herein refers to a hydrocarbon moiety having at least one double bond between two adjacent carbon atoms.
Cyclo alkenyl as used herein refers to a cyclic alkenyl moiety. For example a moiety having the structural formula 
Cyclo alkyl as used herein refers to a cyclic alkyl moiety. For example a moiety having the structural formula 
Arylalkenyl as used herein refers to a moiety having an aryl group and an olefinic group. For example a moiety having the structural formula 
Arylalkyl as used herein refers to a moiety having an aryl group and an olefinic group. For example a moiety having the structural formula 
Alkyl aryl as used herein refers to a moiety having an alkyl group and an aryl group. For a moiety having the structural formula 
Alkenyl aryl as used herein refers to a moiety having an alkenyl group and an aryl group. For example a moiety having the structural formula 
Alkyl aryl alkyl as used herein refers to a moiety having two alkyl groups and an aryl group. For example a moiety having the structural formula 
Acylalkyl as used herein refers to a moiety having an acyl group and an alkyl group. For example a moiety having the structural formula 
Acyl aryl alky as used herein refers to a moiety having an acyl group, an aryl group and an alkyl group. For example a moiety having the formula 